To change the magnetization of a ferromagnet usually requires a magnetic field. So, for example, if we put a compass needle into the high field of an MRI machine, we can no longer trust it to swivel to the North. Similarly, the magnetic stripes on credit cards and key cards can be destroyed in high magnetic fields. Electric fields don’t have the same effect on magnetic materials, which is just as well for everyday applications. However there are specific applications in which the ability to use an electric rather than a magnetic field to produce changes in the magnetization offer distinct advantages. This is because producing tightly focused electric fields is much easier than producing a tightly focused magnetic field. In high density magnetic memories, when we want to switch only one bit (and not all its neighbors), making sure the magnetic field doesn’t spill over requires very careful design.
How can we design materials in which electric fields can change the magnetization? Nebraska MRSEC researchers have demonstrated that this may be achieved by combining a ferroelectric, a material with a permanent electric polarization that produces a large electric field, with a ferromagnet. Using a very thin cobalt film (only a few atoms thick) overlaid with a soft, plastic ferroelectric the researchers altered the direction of the magnetization by switching the polarization of the ferroelectric. Unlike magnetization changes that are achieved using magnetic field, this change in direction is irreversible – switching the electric field back doesn’t change the magnetization. This discovery may lead to electrically controlled magnetic data storage promising higher densities than those available today.